1. Field of the Invention
The present invention generally relates to the fabrication of printed circuit boards and, in a preferred embodiment thereof, more particularly relates to methods for attaching components to printed circuit boards using solder paste and glue dots to operatively mount the components to the substrate portion of a printed circuit board.
2. Description of Related Art
One conventional method of operatively mounting electrical components on a side of a printed circuit board substrate is to deposit on the substrate side, for each of the typically large number of components to be mounted thereon, a spaced pair of solder paste portions on the substrate side and a small quantity of a suitable glue material (typically referred to as a glue "dot") disposed between the solder paste portions and spaced apart from each of them. Typically, the solder paste portions are placed on electrically conductive pads previously secured to the substrate side and operatively coupled to various electrically conductive lead structures that collectively form the electrical circuitry of the board.
After the solder paste portions and glue dots have been placed on the substrate side, the various components to be mounted on the substrate side are sequentially grasped by a high speed "pick and place" machine, moved into alignment with an associated solder paste portion pair and glue dot, pressed against the glue dot and solder paste portions, and then released. After all of the components have been placed on the substrate side (or sides, as the case may be) in this manner, the circuit board is subjected to a final soldering process to permanently secure the mounted components in place. The glue dots, of course, serve to hold the mounted components in place prior to this final soldering process.
Despite the wide use of this conventional component attachment technique as generally described above, it carries with it several well known problems, limitations and disadvantages arising from the method commonly used to apply the usual multiplicity of glue dots to the substrate side(s) prior to the mounting of the electrical components thereon--a single needle type glue dot dispensing machine. This machine functions to apply the requisite glue dots one-by-one via its needle-shaped discharge portion, the discharge portion being moved (typically under the control of a computer) horizontal to the circuit board to a glue dot location, inwardly toward the board to discharge a glue dot thereon, and then away from the board to repeat the cycle on another location thereon.
The problems, limitations and disadvantages of using a needle-type glue dot dispensing machine of this general type include: (1) inconsistently shaped glue dots; (2) an undesirably slow glue dot application rate (typically on the order of about 0.2 seconds/dot); (3) placement inaccuracies that can lead to the glue "stringing" between adjacent conductive pads and creating short circuits in the completed board; (4) missing glue dots created by a clogged dispensing needle; (5) a relatively large manufacturing floor space requirement for the dispensing machine; and (6) a complex computer programming requirement for each different circuit board upon which the dispensing machine is to place glue dots.
In view of the foregoing it can be seen that it would be desirable to provide an improved method for applying glue dots to a circuit board, during fabrication thereof, that eliminates or at least substantially reduces the above-mentioned problems, limitations and disadvantages associated with conventional needle-type glue dot dispensing machines. It is accordingly an object of the present invention to provide such an improved method.